At present, different central suspension devices are known which are applied to rolling vehicles wherein some or all of the vehicle wheels are provided with suspension devices that convert the vertical movement of the wheels into fluid displacement, commonly by the use of simple or double effect conventional hydraulic cylinders. The vertical movements in the vehicle wheels may be due to the unevenness of the ground on which the vehicle is travelling, to the acceleration to which it is subject or to the changes in direction which the vehicle makes when it is going at a certain speed.
Through the fluid conduits, the central devices in question receive the resulting pressure variations of the individual vertical movements of the vehicle wheels. The fluid conduits which come from different wheels are interconnected through fluid shock absorber devices, in such a way that the fluid displacement resulting from the vertical movement of one of the vehicle wheels may be conditional on the fluid displacement of another of the vehicle wheels. Thus, the vehicles are provided with suspension devices that are more or less favourable to bodywork movements involving more than one rolling element or wheel. In the pitching movements of a four-wheeled vehicle, for example, the two front or rear wheels undergo, at the same time, a positive vertical displacement which produces a dipping in the bodywork, which in extreme situations may affect the passenger's comfort and the vehicle's braking capacity, due to the decompensated distribution of the weight of the vehicle on the wheels.
In this case, central devices can avoid a positive displacement occurring and, in turn, on the two front or rear wheels of the vehicle, thus avoiding the excessive dipping of the bodywork and that most of the vehicle's weight is borne by the front wheels.
Therefore, a vehicle's stability is strongly related to the different oscillations that the vehicle body undergoes throughout its ride, which, besides the previously described dipping movements, includes the rocking movements, crossed axles, rotation as regards a vertical axis like rebound (when movements in the same direction occur in all the wheels supporting the vehicle).
In spite of the central devices' response, each of the vehicle wheels should be provided with elastic and individual cushioning means, capable of absorbing the wheel's small vertical movements, such as small potholes or unevenness in the ground, without transferring any movement to the vehicle's other wheels. To date, elastic springs or hydro-pneumatic cavities (hydrospheres) have been used for such purpose. Whereas the first group only works satisfactorily within a very restricted range of dynamic, static and load application situations, thus reducing the wheels' traction capability in the remaining situations, the second group displays a better performance.
The patent document PCT/ES02/00419 discloses a hydraulic suspension device (FIG. 10) between two wheels R1 and R2 made up of two simple-effect hydraulic cylinders 70, 71, connected between the chassis and the wheels wherein the piston 80 and 81 defines an upper cavity 76 and 77 so that the latter undergoes variations in its volume proportional to the movements of each wheel and a double piston device 41 transversally connected to each cylinder through the hydraulic conduits which are connected to the intermediate cavities and of a lesser diameter than the double piston device.
Each cylinder assembled between the vehicle body and the wheels has a hydro-pneumatic cavity 82, 83 which is connected to the cylinder 76, 77 cavity, or to the conduit that joins the latter to the device, providing each wheel with its own elastic component.
The cavity at the end with the greater diameter of the double piston 41 is connected to pneumatic expansion cavity 84 which provides elasticity to the combined movement of both wheels (pitching movement if the latter were the two front wheels of a motor vehicle) whereas it performs rigidly on the reverse movement of both wheels, said movement being limited to the elasticity provided by each of the individual expansion chambers of each wheel.
The hydro-pneumatic cavities usually employed are fitted with a restrictor valve 85 which cushions the flow oscillations of the circuit and uses up part of the energy delivered to or extracted from the compression of a gas 86 stored in its interior and enclosed in an elastic membrane 87.
In spite of the smooth running of the hydro-pneumatic chambers, the membranes 87 which store the gas 86 that the elastic component of the device provides when it compresses or expands undergo a very marked deterioration with the passing of time due to the knocks and friction it bears with the walls of the area surrounding it or with the restrictor valve. The excessive wear and tear of the membrane causes the splitting thereof and a total failure in the performance of the hydro-pneumatic cavity, the individual elastic component of the vehicle wheels being completely lost and therefore a decrease of the control thereof.
Therefore, the absence of a device is felt, which provides the vehicle wheels with an unrestricted movement, without using hydro-pneumatic chambers, and at the same time minimizes lateral oscillation movements, pitching, crossed axles and rocking and which is of a relatively simple construction.